Some small internal combustion engines for handheld power tools such as chain saws, grass trimmers, weed trimmers, leaf blowers, scooters, mopeds, motorcycles and other applications have carburetors that supply a combustible fuel and air mixture to the operating engine. The fuel and air mixture and/or the relative flow rate of the mixture may not be ideal over all operating conditions of the engine. For example, some engines may need additional fuel or a richer fuel/air mixture during acceleration, upon starting or in other conditions.